DE-OS 43 05 405 discloses an apparatus for analyzing an object immersed in a perfusion liquid covering a substrate. The apparatus contains a perfusion chamber which is configured to receive a perfusion liquid via an inlet tank and to draw off the perfusion liquid through an outlet. The inlet of the inlet tank is designed such that an analyzing device can also be introduced into the interior of the perfusion chamber. This known apparatus has the drawback that the perfusion liquid is introduced into the chamber via a funnel-shaped inlet opening and is only drawn off in one direction. Therefore, the chamber is not suited for repeated flushing operations in two directions (forward and backward), nor for a subsequent removal of the objects. Moreover, the chamber is also not suited as a single-use article for sterile operations, e.g. with cell cultures, because of the complex and time consuming drilling and milling associated with the manufacturing method used for the chamber.
An improvement over the known perfusion chambers is described in DE-OS 43 21 062. For perfusion treatment, in particular of biological objects, the objects are exposed to a directed liquid flow having a defined area of operation. The liquid flow is formed by two suitably combined pipette tip members or an applicator member shown for illustrative purposes in FIG. 7. The applicator member is an annular component 70 having a specifically designed pipette tip member 71 which differs from conventional pipette tip members in that it has a curvature and is directly connected to the wall of annular component 70, thereby forming a perfusion liquid inlet. A liquid conveying device 72 is removably attached to the pipette tip member 71. The applicator member can be attached with a lower sealing edge onto a substrate 74 to enclose the substrate 74 to be treated. The perfusion treatment involves, in particular, the alternate discharge and drawing of perfusion liquid through the pipette tip member.
The apparatuses described in DE-OS 43 21 062 have the drawback of requiring manipulation of conventional pipette tip members. Conventional pipette tip members (i.e. easily manufactured members that taper toward the tip without any curvature and are regularly used for metering and proportioning liquids) must be used either in the combination (i.e., two pipette tips are positioned together or even attached and operated by two liquid conveying devices) or a special applicator member has to be manufactured in the case where the pipette tip member is connected to an annular component.
The applicator member described in DE-OS 43 21 062 and shown in FIG. 7 has the following further drawbacks. The applicator member has an asymmetric shape with curved portions that do not permit any simple injection molding manufacturing processes to be used. Because of the nature of the connection between the annular component 70 and the pipette tip member 71 this device is not suitable for precise handling of liquids and suspensions. Specifically, adhesive forces at the inner and outer surface of the annular ring create an undesired "dead" volume of perfusion liquid (perfusion liquid that adheres to the annular ring and therefore is not utilized in the treatment process). The dead volume practically excludes the handling of precise liquid volumes with the device shown in FIG. 7. Further, the undesired dead volume creates cleaning problems.
Since conventional pipette tip members which are suitable for precise liquid handling and attachable to a liquid conveying device (such as "Costar," "Eppendorf" (Germany) and "Gilson" (France) pipettes) cannot be used in the DE-OS 4321 062 device, the applicator member must be adapted to the respective liquid conveying device 72. Hence, a large-scale production of universally usable applicator members is not possible. The structure of the known applicator member leads to mechanical instability due to the lever effect of the pipette tip member 71 on the curved portion, which is detrimental to the sealing of the lower edge of the applicator member 70 relative to the substrate 73 and to its use in automated systems. The asymmetric form of the applicator member is in general difficult to handle, because a mounting of the applicator member on the liquid conveying device always necessitates alignment of the two members and is not suitable for precise handling of liquid volumes.
Due to the drawbacks described above, known applicator members have so far only been used in laboratories. However, rapid progress in analytic methods for genetic engineering have created great interest in perfusion devices that can be mass-produced, and that can be reliably and automatically operated. The above-mentioned drawbacks are found not only in perfusion devices, but generally in all devices used for treating objects within a defined treatment area in a liquid bath (e.g. perfused, diluted, flushed, partially dissolved, mixed, removed or the like), as well as in apparatuses used for mixing liquids.